The present invention relates to a multi-layer headbox comprising a narrowing slice cone and separation lamellae extending from flaps out of the discharge opening of the slice cone.
In the operation of prior art multi-layer headboxes, so-called impurity of layers has been noticed, i.e., different layers tend to be mixed together or to be distributed unevenly. This phenomenon has been noticed in particular in multi-layer headboxes in which there is an intensively narrowing slice cone. In this type of headbox, the outer stock layers change their direction when they come out of the narrowing slice cone through the discharge opening to form parallel discharge jets. This change in direction produces so-called secondary vortices, which further produce vanes, i.e. the impurity of layers and uneven distribution of layers mentioned above. For example, the middle layer tends to be mixed with the surface layer. These secondary vortices are produced by the change in the flow direction on the curved face of the flap.